A2K is free software; you can redistribute it and/or modify it under the
terms of the GNU General Public License as published by the Free
Software Foundation; either version 2 of the License, or (at your
option) any later version. This program is distributed in the hope that
it will be useful, but without any warranty; without even the
implied warranty of merchantability or fitness for a
particular purpose. See the GNU General Public License for more
details. You should have received a copy of the GNU General Public
License along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

A Transparent copy of this manual (as defined by the GNU Free
Documentation License) is included in the A2K distribution, available
from the A2K web site.

Introduction

A2K is a small, simple, and unobtrusive IRC bot. It differs from the
other n+1 IRC bots out there in that it is meant to do only a few
things, do them well, and generally be seen and not heard. A2K offers
the following features:

An automatic channel-operator management system.

A URL catcher, which records URLs seen on the channel in a file.

A system for changing A2K's configuration while it is
running.

An appetite for botsnacks. (Botsnacks are an optional method for
indicating that A2K is listening and functioning properly. If botsnacks
are activated, A2K will smile when it hears the word "botsnack" on the
same line as its nick (i.e. "a2k, have a botsnack.") This is one of
the only situations in which A2K says anything to the IRC
channel.)

Why the name A2K? Originally this was called Accutron 2000; however,
Accutron is a brand of watches manufactured by Bulova, and the name was
changed to avoid confusion with their trademark. A2K is not an acronym;
it does not stand for anything.

WARNING: The Surgeon General has determined that taking IRC too
seriously is dangerous to your health.

Installation

A2K is written in Python. It has been
tested on Solaris (2.6/7/8), Red Hat Linux (6.2/7.0) and Microsoft
Windows (98) with Python versions 1.5.2, 1.6 and 2.0.

A2K is free software, distributed under the terms of the GNU
General Public License from the
A2K web site.

A2K requires no unusual installation procedure; simply extract the
distribution archive into a directory. It is recommended that you keep
all of the distributed files in the same directory. You should have the
following files:

Configuring And Starting A2K

You will need to configure A2K before running it for the first time. All
options are set in the a2kconf.py file. A2K will refuse to run if
certain options are not configured. You must change these from
their default values.

The Configuration Module

The a2kconf.py file contains all of A2K's configurable
options. You should set each one of these options to define the
identity, home, and other features of A2K. Be careful when editing
a2kconf.py to maintain the syntax in the file.

These are the options configured in a2kconf.py:

server: This is a list of hostnames and ports of IRC servers
that A2K should connect to. On startup, it will connect to the first
hostname and port in the list. In order for the jump command
to be useful, there should be at least two hostname/port tuples in this
list.

nick: This is the nickname that A2K should use. The IRC
protocol says it should be nine characters or less, but many IRC servers
permit longer nicknames.

name: This is the "real name" A2K should use. For instance,
if nick is "jdoe", name might be "John Doe".

channel: This is the IRC channel that A2K should join. IRC
channels usually start with the "#" character.

chanmodes: This is a set of IRC channel modes that A2K should
set when joining channel, if it can. For instance, "+nt-i"
would result in A2K setting the "n" and "t" modes, and clearing the
"i" mode.

botsnacks: This specifies whether A2K should eat botsnacks. Set
to 0 to disable, or 1 to enable. When enabled, A2K will smile whenever
the word "botsnack" is said on the IRC channel.

password: This is a password that will be required when sending
commands to A2K. This password will be sent in clear text via the IRC
server, so it should not be a password you use for anything valuable.

urllist: This is a filename where A2K will write URLs that
appear on the IRC channel. The format of this file is standard HTML. If
it does not exist when A2K starts running, it will be created.

opdelay: This specifies the number of seconds that A2K will
wait before giving ops to someone joining the channel. It is recommended
that you not set this to 0. The default is 5.

The Op List

The a2kconf.py file also contains the list of channel
operators. A2K will give channel operator status to users who match the
criteria specified in this file. You should list all of the users who
are to receive channel operator privileges.

A2K uses regular expressions to specify the username and hostname
patterns that correspond to valid channel operators. If you are
unfamiliar with regular expressions, please consult a reference such as
Mastering Regular Expressions by Jeffrey E.E. Friedl, published
by O'Reilly And Associates.

The channel operator list is kept in a Python data structure called a
"dictionary". Each item in a dictionary has a key and a definition. In
our case, the key is an IRC nickname, and the definition is a regular
expression which the nickname's user and host must match. For instance,
suppose there is a user named Bullwinkle J. Moose at Wassamatta U. He
uses the nickname "bullwinkle" and should get channel operator
privileges when connecting from machines in the "wassamatta.edu"
domain, where his login is "moose". In the operator list, his key
would be "bullwinkle" and a good definition would be
"moose@.*\.wassamatta\.edu".

a2kconf.py contains several lines of the form

op['key'] = re.compile('definition')

where key and definition are as specified above. To continue
the Bullwinkle example, his entry in a2kconf.py would look like
this:

op['bullwinkle'] = re.compile('moose@.*\.wassamatta\.edu')

And his friend Rocket J. Squirrel, whose login at Wassamatta is
"squirrel" and whose nickname is "rocky", might have an entry like:

op['rocky'] = re.compile('squirrel@.*\.wassamatta\.edu')

However, consider the case of Natasha Fatale, nickname "natasha", who
is not only attending Wassamatta U., where her login is "fatale", but
uses AOL as well, where her screen name is also "fatale". Her entry
might look like:

As you can see, using regular expressions for the patterns to be matched
allows a fair amount of flexibility and complexity.

You should have one line similar to the above in a2kconf.py for
each individual user who is to receive channel operator privileges.

Starting A2K

After editing the a2kconf.py file, A2K is ready to run. To start
A2K, instruct your Python interpreter to run a2k.py. On UNIX
systems, you can run a2k.py directly if the Python interpreter is
in your path. On Microsoft Windows systems, you can double-click the
a2k icon.

A2K normally produces no output. You will know that A2K is running when
you see it join the channel you specified, using the nickname you
specified.

A2K Commands

If you are listed in A2K's op list, you can send commands to A2K to
alter its behavior while it is running. To do this, you send a private
message to the bot's nickname. The message should be in the following
format: passwordcommandarguments, where
password is the password specified in a2kconf.py,
command is a command from the following list, and
arguments is one or more arguments required by the
command. (Some commands take no arguments; you would omit
arguments in this case.)

These are the commands currently understood by A2K:

die: Causes A2K to stop running. The bot will disconnect from
the IRC server.

addop nicknameregexp: Adds an entry to the
channel operator list for the nickname specified. regexp should
be a regular expression in the same format used in a2kconf.py. If
there is already an entry for nickname, it is replaced by the
new one.

delop nickname: Deletes the entry for
nickname from the channel operator list, if such an entry
exists. If no such entry exists, you will be notified.

showop nickname: Shows you the entry for
nickname from the channel operator list, if such an entry
exists. If no such entry exists, you will be notified.

jump: Causes A2K to disconnect from its current server and
connect to the next server in its list. If you have only one server
defined, this command disconnects and then immediately reconnects to the
same server. This is useless, but benign.

nick nickname: Changes A2K's nickname to
nickname.

passwd password: Changes the password used to
authenticate these commands to password.

writeconf: Writes the current configuration to
a2kconf.py. Do this to make changes made via addop,
delop, nick, server and/or
passwd permanent.

botsnacks: Turn botsnack consumption on. A2K will smile when
"botsnack" is heard on the IRC channel.

nobotsnacks: Turn botsnack consumption off. A2K will not smile
when "botsnack" is heard on the IRC channel.

cycleurls backupname: Renames the urllist file to
backupname, and starts a new urllist file. Useful when the
urllist file starts getting a little long.

inviteme: Requests an invitation to the channel. If the person
requesting the invite is on the op list, A2K will issue the invite
itself; otherwise, it will send a notice to the channel saying that an
invite has been requested (and someone else will have to do the actual
inviting.) This is, obviously, useful iff mode +i is set on the
channel. Note: This command does not require a password; do not
specify one. The entire contents of the message to A2K should be
"inviteme".

The URL Catcher

The URL catcher records URLs that A2K sees on its IRC channel in a
file. This file can be placed anywhere on your system; use the
urllist option in a2kconf.py to specify its
location. Any given URL will be recorded only once. Also, all URLs are
checked for validity before being recorded. URLs requiring
authentication (username and password) are not recorded. Finally, only
URLs beginning in http://, https://ftp:// and
gopher:// are recorded. If a URL does not seem to be caught by
A2K, bear these conditions in mind.

Note that URLs beginning in https:// are only recorded if your
Python interpreter was configured to support the HTTPS protocol. This
is not always the case, depending on your platform and Python version.
Python 1.5.2 as shipped with Red Hat Linux 7 works with HTTPS, and could
perhaps be used as an example case if you are building Python to support
this feature.

Commentary

Bad attitude ahead! Do not read this chapter if you are easily
annoyed or offended.

Some may wonder why A2K was written when there are many other IRC bots
available. I frequent a channel which I won't name here (it's private)
except as The Channel Which Must Not Be Named. On TCWMNBN, we needed a
bot that would handle just a few things without excessive 3l33t s+uph or
other kitchen-sink capabilities. Because our hubris was strong, we
decided to write our own. Our first attempt at this was called
"foetus", and worked pretty well but grew into a monstrously
unmaintainable Perl script. Later, I ripped out almost all of foetus and
created a smaller, leaner version called "reify" which was meant to do
just a few things but do them well. After reify fell into disrepair, I
started writing A2K from scratch. I could have fixed reify instead, but
I've been away from it for a long, long time. In the meantime, it seemed
to have stopped working with the latest Net::IRC modules, and I'm not
sure if that's reify's fault or Net::IRC's fault (Net::IRC always was a
little buggy in spots.) Plus, I wanted to do a project that would teach
me about raw socket I/O. And I wanted to do it in Python. So there. :)

OK, so there are n+1 other IRC bots available already. It was the
vogue project for a while (until people started writing lots of ICQ
clients and MP3 rippers...) You've got Eggdrop which does just about
anything, you've got Infobot which gathers information, and you've got
31337 w4r b0tZ for the antisocial IRC crowd. A2K is none of the above:
it is a simple, useful bot which doesn't pretend to do a lot of things
that really aren't necessary for what I need in a bot. It only does a
few things, and tries to do them well. Does it succeed? So far, yeah,
more or less. Of course, that's just my opinion. If A2K isn't up to
snuff for whatever you use bots for, feel free to not use it. But I have
a feeling I'm not the only one with these requirements.

A2K's feature set corresponds to the somewhat limited requirements I
have for it. If it doesn't do X, Y or Z that you want it to, well, this
is a GPL licensed program, feel free to hack it around until it meets
your requirements. You can send me patches but I may or may not include
them - it depends on whether I personally feel they improve the
program. For instance, code that improves A2K's ability to deal with net
splits has a better chance of getting in than code that implements XDCC
warez sharing with integrated leech ping-flooding. Of course, if X Y or
Z is something that I wanted it to do, and it doesn't, that's
probably a bug, and I want to hear about it.

On TCWMNBN, there are only two types of users: those with ops, and those
without (and those without are rare, as TCWMNBN is private and we don't
get a lot of visitors.) So I have no need to create multiple levels of
eliteness, as in other bots such as Eggdrop. If you want the
functionality of Eggdrop, use Eggdrop.

A2K may not work on all IRC networks. If you can provide me with a patch
that makes it work on a given IRC network, I'll probably include it, but
I only test A2K on one network (The Network Which Must Not Be Named,
which uses ircd-hybrid) and if it works there for me, it's all good as
far as I'm concerned.

As you may know, many IRC operators and networks don't like bots. If
they don't want bots on their servers, that's their prerogative. If you
get yourself K-lined somewhere because you were running A2K against the
rules of that server/net/whatever, well, tough titty, I don't want to
hear about it. I will not add any code to make A2K appear to
not be a bot; this is a decent, well-behaved bot, dammit, not an 3l33t
w4r h4qr b0t.

I apologize if that last paragraph put you off. I just see too much
stupidity on the net these days and I felt the need to make a preemptive
strike or two. I hope you like A2K and that you find it useful;
otherwise, I wouldn't be releasing it, now would I? All I ask is that
you have a clue. Hopefully you've got a clue now. If not, let me know
and I'll try harder. Really, I'm a nice guy, I just don't like dealing
with stupidity.

Dedications

A2K is dedicated to the men and women of The Channel Which Must Not Be
Named, who benefit from my work yet chronically ignore it because it has
nothing to do with the Dreamcast. I am nothing if not selfless.

The purpose of this License is to make a manual, textbook, or other
written document free in the sense of freedom: to assure everyone
the effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially. Secondarily,
this License preserves for the author and publisher a way to get
credit for their work, while not being considered responsible for
modifications made by others.

This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.

We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals;
it can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
principally for works whose purpose is instruction or reference.

APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work that contains a
notice placed by the copyright holder saying it can be distributed
under the terms of this License. The "Document", below, refers to any
such manual or work. Any member of the public is a licensee, and is
addressed as "you".

A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.

A "Secondary Section" is a named appendix or a front-matter section of
the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall subject
(or to related matters) and contains nothing that could fall directly
within that overall subject. (For example, if the Document is in part a
textbook of mathematics, a Secondary Section may not explain any
mathematics.) The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.

The "Invariant Sections" are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License.

The "Cover Texts" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License.

A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
general public, whose contents can be viewed and edited directly and
straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file
format whose markup has been designed to thwart or discourage
subsequent modification by readers is not Transparent. A copy that is
not "Transparent" is called "Opaque".

Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format,
SGML or XML using a publicly available
DTD, and standard-conforming simple HTML designed
for human modification. Opaque formats include PostScript,
PDF, proprietary formats that can be read and edited only by
proprietary word processors, SGML or XML for which
the DTD and/or processing tools are not generally available,
and the machine-generated HTML produced by some word
processors for output purposes only.

The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.

VERBATIM COPYING

You may copy and distribute the Document in any medium, either
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no other
conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.

You may also lend copies, under the same conditions stated above, and
you may publicly display copies.

COPYING IN QUANTITY

If you publish printed copies of the Document numbering more than 100,
and the Document's license notice requires Cover Texts, you must enclose
the copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify
you as the publisher of these copies. The front cover must present
the full title with all words of the title equally prominent and
visible. You may add other material on the covers in addition.
Copying with changes limited to the covers, as long as they preserve
the title of the Document and satisfy these conditions, can be treated
as verbatim copying in other respects.

If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.

If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a publicly-accessible computer-network location containing a complete
Transparent copy of the Document, free of added material, which the
general network-using public has access to download anonymously at no
charge using public-standard network protocols. If you use the latter
option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this
Transparent copy will remain thus accessible at the stated location
until at least one year after the last time you distribute an Opaque
copy (directly or through your agents or retailers) of that edition to
the public.

It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to give
them a chance to provide you with an updated version of the Document.

MODIFICATIONS

You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:

Use in the Title Page (and on the covers, if any) a title distinct
from that of the Document, and from those of previous versions
(which should, if there were any, be listed in the History section
of the Document). You may use the same title as a previous version
if the original publisher of that version gives permission.

List on the Title Page, as authors, one or more persons or entities
responsible for authorship of the modifications in the Modified
Version, together with at least five of the principal authors of the
Document (all of its principal authors, if it has less than five).

State on the Title page the name of the publisher of the
Modified Version, as the publisher.

Preserve all the copyright notices of the Document.

Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.

Include, immediately after the copyright notices, a license notice
giving the public permission to use the Modified Version under the
terms of this License, in the form shown in the Addendum below.

Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.

Include an unaltered copy of this License.

Preserve the section entitled "History", and its title, and add to
it an item stating at least the title, year, new authors, and
publisher of the Modified Version as given on the Title Page. If
there is no section entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.

Preserve the network location, if any, given in the Document for
public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions
it was based on. These may be placed in the "History" section.
You may omit a network location for a work that was published at
least four years before the Document itself, or if the original
publisher of the version it refers to gives permission.

In any section entitled "Acknowledgments" or "Dedications",
preserve the section's title, and preserve in the section all the
substance and tone of each of the contributor acknowledgments
and/or dedications given therein.

Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers
or the equivalent are not considered part of the section titles.

Delete any section entitled "Endorsements". Such a section
may not be included in the Modified Version.

Do not retitle any existing section as "Endorsements"
or to conflict in title with any Invariant Section.

If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.

You may add a section entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties--for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.

You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.

COMBINING DOCUMENTS

You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice.

The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.

In the combination, you must combine any sections entitled "History"
in the various original documents, forming one section entitled
"History"; likewise combine any sections entitled "Acknowledgments",
and any sections entitled "Dedications". You must delete all sections
entitled "Endorsements."

COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents
released under this License, and replace the individual copies of this
License in the various documents with a single copy that is included in
the collection, provided that you follow the rules of this License for
verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute
it individually under this License, provided you insert a copy of this
License into the extracted document, and follow this License in all
other respects regarding verbatim copying of that document.

AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, does not as a whole count as a Modified Version
of the Document, provided no compilation copyright is claimed for the
compilation. Such a compilation is called an "aggregate", and this
License does not apply to the other self-contained works thus compiled
with the Document, on account of their being thus compiled, if they
are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one quarter
of the entire aggregate, the Document's Cover Texts may be placed on
covers that surround only the Document within the aggregate.
Otherwise they must appear on covers around the whole aggregate.

TRANSLATION

Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License provided that you also include the
original English version of this License. In case of a disagreement
between the translation and the original English version of this
License, the original English version will prevail.

TERMINATION

You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.

FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions
of the GNU Free Documentation License from time to time. Such new
versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and
license notices just after the title page:

Copyright (C) yearyour name.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1
or any later version published by the Free Software Foundation;
with the Invariant Sections being list their titles, with the
Front-Cover Texts being list, and with the Back-Cover Texts being list.
A copy of the license is included in the section entitled ``GNU
Free Documentation License''.

If you have no Invariant Sections, write "with no Invariant Sections"
instead of saying which ones are invariant. If you have no
Front-Cover Texts, write "no Front-Cover Texts" instead of
"Front-Cover Texts being list"; likewise for Back-Cover Texts.

If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License,
to permit their use in free software.